In a letter addressed to the family of the man shot and killed by a police officer in Ferguson, Mo., Trayvon Martin's mother extended a sympathetic arm and welcomed them to the "exclusive yet growing group of parents and relatives who have lost loved ones to senseless gun violence."

Brown, who was unarmed, was shot and killed by Missouri police officer Darren Wilson on Aug. 9. One of Brown's three autopsies revealed that he was shot at least six times in various parts of his body, including the top of his head.

"Further complicating the pain and loss in this tragedy is the fact that the killer of your son is alive, known, and currently free," Fulton wrote in the letter.

Brown's death sparked daily protests in Ferguson and across the country. Although the protests have been largely peaceful, rioting, looting and property damage also has been reported.

Missouri Gov. Jay Nixon on Saturday declared a state of emergency and enforced a curfew. After the heavily militarized police presence initially sparked more unrest from protesters and national observers, Nixon then replaced local police units with Missouri State Highway Patrol units, and he eventually had to call in the National Guard today to help control protesters.

"Your circle will necessarily close tighter because the trust you once, if ever had, in 'the system' and their agents are forever changed," Fulton wrote in her letter. "Your lives are forever changed ... I know this because I lived and continue to live this."

Fulton's son, Trayvon, was shot and killed by neighborhood watch volunteer George Zimmerman in 2012. The following year, a jury found Zimmerman not guilty of second-degree murder in the unarmed 17-year-old boy's death.

Zimmerman's aquital was met with protests both locally and nationally.

"If they refuse to hear us, we will make them feel us," Fulton wrote in closing. "Feeling us means feeling our pain; imagining our plight as parents of slain children. We will no longer be ignored."

Benjamin Crump, the Tallahassee attorney who represented Trayvon's family now represents Brown's family, as well.

The former associate medical examiner who autopsied Trayvon Martin and Marlon Brown has released an ebook, accusing police and prosecutors of deliberately suppressing, destroying or ignoring evidence in those cases.